Multipole magnets consist of a plurality of magnetic poles and, among other things, are used to deflect, focus or otherwise alter the characteristics of beams of charged particles in particle accelerators. Multipole magnets may be used to change the overall direction of a beam, focus or defocus a beam, or correct aberrations in a beam. The suitability of a multipole magnet for performing these tasks is determined largely by the number of magnetic poles present. Quadrupole magnets having four magnetic poles, for example, are particularly suitable for focusing and defocusing a beam of charged particles. In modern particle accelerator beamlines, hundreds of multipole magnets may be employed along a single beamline. In proposed future beamlines, thousands of multipole magnets are likely to be required for a single beamline.
The magnets used in multipole magnet arrangements may be electromagnets, consisting of a current carrying wire coiled around a ferromagnetic pole, or permanent magnets, which are inherently magnetized.
Electromagnets typically require an expensive power supply and may also require cooling means to remove the heat produced by the current carrying coils. The cooling means may comprise, for example, a plumbing system capable of circulating a coolant, or an airflow system for circulating cooled air. Any cooling system will incur additional set-up and running costs associated with each multipole magnet and will also require sufficient space around the multipole magnets in which to operate.
In contrast, permanent magnet multipole magnets do not require a power supply or a cooling system. An example of a permanent magnet multipole magnet is described in US-A-2002/0158736 (Gottschalk S. C.). The Gottschalk multipole magnet includes a plurality of ferromagnetic poles and one or more permanent magnets that are moveable relative to the poles to produce a variable magnetic field between the poles.
It is an object of the present invention to provide an improved multipole magnet that includes permanent magnets and is advantageous over the multipole magnets of the prior art.